Nuptials
by Leafenclaw
Summary: "Me and Jim Moriarty, we got on like a house on fire," says Eurus to Sherlock five years later. Because one of the most underrated pleasures of being the youngest sibling is messing with your older brother.


_**Disclaimer: Everything you recognises belongs to someone else. I'm just playing here.  
**_

**A/N: **For Criminally/Doaa. Prompt was: "Jim and Eurus get married for the sole purpose of terrifying Mycroft and make his life miserable."

**Warnings:** I'd say Eurus and Jim come with their own warning labels, but aside from a mention of canon violent acts, you should be good. Please tell me if there's any trigger warnings I should add.

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**Nuptials**

When the surveillance equipment comes back online, Mycroft wonders for a moment if all the hair he pulled in those unsupervised five minutes is ever likely to grow back. To his endless chagrin, he realises it probably won't. Stress will kill him first.

On the video feed, Moriarty is standing _far _past the restricted area. For a second Mycroft squints helplessly, trying to see his sister over the man's shoulder, before he remembers there is more than one camera in the room. Cold sweat beads on his temples when he switches the feed's point of view. They stand so close to each other that, were they not separated by a thick piece of glass, they could be sharing an embrace.

_Yep. Stress, or a heart attack._

"If we go through with his, we will require a friendly priest," says Eurus.

Her voice, distorted by the speakers, comes softer than it probably is.

Or so Mycroft hopes. The idea of her speaking so tenderly to Moriarty – to _anyone_, if he's being honest – alarms him on a level impossible to describe. He remembers all too well what happened the last time she got close to another human being.

_Make that _all the times _she got close to anyone. _

"What do you mean, _'if'? _I gave you my word!"

Moriarty's voice on the other hand is oozing playfulness and menace, a particular blend Mycroft has grown accustomed and deeply allergic to over the last few months.

"Perhaps. But your word isn't the one I doubt," answers Eurus. "Isn't it traditional to secure permission from the girl's family first?"

Moriarty takes a step back, brings a hand up – taps a finger against his lips, Mycroft thinks, but he cannot be sure until he hastily switches camera viewpoints again, and by the time he does the man's hand is already back down.

"Fair enough," grins Moriarty. "But that's never gonna happen. So we'll have to elope."

"I suppose, yes. And priests are the best option when seeking shelter, are they not?"

"Two birds with one stone! I like the way you think."

Eurus smiles sweetly.

"Oh, I know," she says, eyes suddenly shining. "We should ask Sherlock to officiate. He has a flat we could hide in, and – he's still a virgin, isn't he? That's close enough to a priest."

Mycroft shivers, gets up from his desk. He hadn't intended to go down there at first, but sending guards to retrieve the man on their own would be a security risk – he doesn't trust his sister one bit, certainly never trusted Moriarty, and their cosy conversation is making him deeply uncomfortable. If she could convince an upstanding man to commit murder within ten minutes of a casual conversation as a child, who knows in what ways she made this particular criminal even more dangerous than he was when he went in?

(Deep inside Mycroft realises there is something deeply conceited to the idea that he might be able to stop them on his own – Eurus' capacities always by far surpassed his own, and Moriarty has his own level of brilliance, together they would be unstoppable, and oh, how terrifying would that be? – but he has always rightly owned the privilege of arrogance, and he certainly stands a better chance than any of those guards with puny intellects.

Doesn't he?)

Their conversation comes clear across the headset in Mycroft's ears, even as he leaves his office and takes the long ride down the elevator. Two men quickly fall in line behind him, both armed to the teeth. They don't make him feel any better, but he allows their presence – sending them away to go down there alone would be worse.

Probably.

"Oh, he won't stay a virgin for long. But yeah, he'll do. I know for a fact he makes a _mean _priest."

"I _like _the mean ones."

"All banged up and bloodied, with eyes everywhere they shouldn't be," sing-songs Moriarty.

Eurus' giggle sends cold sweat sliding down Mycroft's spine.

"Will you bring me a ring, then, the next time we meet?"

"I thought you might prefer a key. But I will, if you want one. Would titanium do? Coupled with diamonds, the symbolism is de-_light_-ful. We could engrave it with – "

"_Wait!_"

A loud banging noise makes Mycroft jump. The guard on his left touches the gun hanging off his hip, but he raises a hand, points to his headset. The man nods, backs down. Mycroft pinches his lips.

_The glass. One of them hit the glass with – something. Fist? Chair? Or a kick maybe? There's no way to tell until I get there. And even then_ –

"Rings are like... handcuffs for the fingers, aren't they?" says Eurus, interrupting his thoughts, a pondering inflexion to her voice.

Too calm to have hit the glass herself, Mycroft thinks, but it's not as if someone – human or machine – has ever been able to read Eurus properly. Nobody can. He doesn't think anybody ever will.

(Her cardiac rhythm never reached over 70 when she was butchering her first sexual partner, and yet it was well over 100 when she requested her Christmas gift last week. Sometimes he wonders if that wasn't a deliberate attempt to recreate one of Hannibal Lecter's feats. She did request the complete collection of Thomas Harris' works a few years back, and she's been known to quote them before. It shouldn't be surprising that she enjoys making herself unsettling by design.

Not that she needs to mimic the actions of a fictional cannibal to obtain _that _reaction, but he's certainly not about to admit that out loud.)

"No," Eurus adds in his headset. "I don't think I would enjoy a ring very much, after all."

"But it's traditional! You can't get married without a ring."

_Married? What the... That damn elevator isn't quick enough!_

"Yes, I know. But I don't want one."

"Seems we've hit a snag, then."

"Does _everything _have to be traditional?" whines Eurus.

"Why, I thought that's what you wanted."

A beat of silence.

"You're right. It is. But my fingers deserve freedom. Perhaps a _key_ring would do instead?"

Moriarty's laugh comes warm and open, a jarring contrast with his personality – or rather with the sliver of it he exposed around Mycroft, who shivers again, eager to put a stop to whatever that conversation is about.

"Keyring it is, then. How about little roses to hang on it? That would be cute. Play off your charm."

"No, roses are boring."

"Hearts then? Nothing like hearts to show off your love for all to see."

"Too bloody. I think I would prefer a skull. Bones are much cleaner."

"How cliché."

"A fruit then, I hear lovers feed them to each others."

"Alright. Which one?"

"You choose."

"How about an apple?"

"The poisoned kind?"

"Obviously."

"Who is being cliché now?"

Moriarty laughs again.

"I do so love my fairy tales."

"Fine. An apple keyring, that would be suitable. Not silver though – tarnishes so easily. Pewter, perhaps. And real flowers, so I can put them in my hair."

"Oh _yes_, that would be lovely. You have such beautiful hair, darling. Dark, shiny, curly, just like – "

" – _Sherlock!_" they say together, an eerie, off-key harmony of tenderness and laughter.

The elevator finally stops on the last floor. Mycroft rushes along the hallways past security, barely catches the guards' chatter overhead on the intercom, too busy trying to hear his sister's and her guest's – _gift's_ – conversation. But there isn't a single sound coming from his headset anymore, and the silence scares him more than any dialogue would.

When he finally reaches Eurus' room, the first thing he sees is Moriarty leaning forward, both hands and forehead pressed against the glass, and in front of him the lean, white form of his sister doing the same. Humidity fogs the area around their mouth, an illusion of shared breath, and when Moriarty turns his head towards him, his eyes are dark, bottomless pits of unfathomable depths – a lurid expression, Mycroft thinks, and yet the only one that fully captures the spectacle in front of him.

The sheer intimacy of them – what has he just interrupted?

For half a second he wonders if they didn't find a way to have sex – then dismisses the idea. The glass panel is still intact. So is – sadly – the man standing before it. Yet the notion frightens him so much that for a brief moment his throat is startled into dryness, and he bites his tongue twice before his body remembers how language works.

"Step away from the glass _immediately_," he says, trying for stern, but unable to keep a hint of fear from raising the overall pitch of his voice.

"Brother dear!" says Eurus, smiling at him over Moriarty's shoulder. "Why so serious?"

"Ooooooh, that's a nice one," chuckles Moriarty, bouncing on his toes. "I didn't think you were allowed movies down here."

"Oh yes. Birthday presents are always movie."

"Did you see Star Wars?"

"The first three, as a child. I hear they made sequels, are they any good?"

"Nah, you can skip those. Star Trek?"

"No. Should I?"

"Definitely! Oh, you're gonna _love _it, trust me. Wait 'til you see _that _scene with Spock where – "

"_Step away from the glass!_" Mycroft repeats loudly. "I won't ask a third time."

The guard on his right engages his gun, the characteristic click-clack punctuating his words. The noise is met by twin laughter. Mycroft nearly rolls his eyes. He could have _told _them those tactics weren't likely to work, not with those two.

"It's okay, Jim," mock-whispers Eurus, her voice still coming loud through the speakers. "I hate spoilers anyway."

"Yeah, you would," answers Moriarty – stepping back as requested, but gazing at her with affection and tenderness and deep longing and _what the hell._ "Besides, we're getting a little side-tracked, aren't we?"

"Oh, you're right. I almost forgot. Brother dear! I'm getting married!"

Mycroft nearly gapes at them. The only thing that ultimately stops him from floundering uselessly is the spark of mischief hidden in Moriarty's knowing smirk – the one that makes him appear just a little too eager. He's waiting for a reaction, that much is obvious, and Mycroft is determined not to give him one.

_Heart attack. Yeah. It's the heart attack that'll get me. Marriage, sweet baby Jesus._

"What did you just say?" he asks softly, carefully controlled.

"A wedding, big man," answers Moriarty. "Surely you know how _that _works."

"Jim proposed. I accepted. It seemed like the reasonable thing to do, since he came so far just to ask for my hand."

"She's such a sweet girl. How could I not?"

"Not that I plan to give him my hand _literally_. I might still need both of them."

"It's okay. I have two of my own already."

They grin at each other, and suddenly the floor doesn't seem as stable as it felt just a few minutes ago.

"Just – slow down," Mycroft says, resisting the urge to rub at his temples. "You only _just met_."

(A tiny, distant part of his brain is aware that, of all the arguments to raise against this specific union, "you only just met" was probably the weakest one. The largest part of his mind, still trying to process what the hell is going on, doesn't really care what kind of arguments to raise as long as he comes up with one.

Or several thousand.

_Jesus_.)

"Oh, we'll have a long courtship, of course," says Moriarty, one hand rotating aimlessly in the air. "It'll take at least a year to organise the ceremony. Right honey?"

"Maybe even up to five," answers Eurus, her smile downright chilling.

"But I have to admit, Mycroft – I can call you Mycroft now, right? Since our families are about to be joined in matrimony? I am _so _looking forward to being your brother-in-law."

Moriarty's wolfish grin, coupled with those words, is what ultimately snaps his brain back to attention.

_They're toying with me. I don't have to play that game. _

"_Enough_ with your nonsense. Eurus, say goodbye to your Christmas present, it's time for him to go home."

"Shame," answers his sister with a wistful expression. "I was hoping we could negotiate terms for a family dinner this year. Oh well. Elopement it is. Goodbye, Jim. It was nice meeting you."

"My dear, it was _entirely_ my pleasure."

"Don't worry," she giggles. "I'll put in a request for next year."

"And in the meantime, I'll – arrange everything else."

"I know you will."

Eurus cocks her head to the side, then smiles, sad and serene and utterly terrifying. Moriarty drops into a formal half bow, then blows a kiss in her direction, eyes shining like scarab shells. It takes all of Mycroft's self-control not to manhandle him out of the room himself.

"Beautiful creature, your sister," he says as they walk out, a hint of teeth glittering sharp and self-satisfied. "A lifetime in the company of a Holmes sibling? I couldn't dream a better outcome for myself. Present company excepted, of course," he adds like an afterthought. "No offence. You're not really my type."

"Whatever you're playing at, _it stops now_," Mycroft hisses in response. "You're never gonna see her again if I can do anything about it, and I have enough resources at my disposal to safely say that _I do_."

"Yeaaaah... You're right. I suppose there _are _unsafe ways to say 'I do'."

His voice is light and thoughtful and utterly despicable and Mycroft wants nothing more than to strangle him.

"So if I understand you well," Moriarty adds before he can give in to the urge. "You plan to deny her next Christmas request? Not very brotherly of you, isn't it?"

Mycroft takes a deep, steadying breath.

"I could, but I won't need to."

"Oh yeah?"

"I won't need to because _you _will be the one doing it for me. Next Christmas, you'll stay very far away from Sherrinford. So far away I won't even have a chance to find you. That way I won't be lying when I tell her you were unavailable."

Moriarty laughs.

"Oh, look at you, Iceman. So _tough! _Bringing out the big guns now, huh? How long did you rehearse that little 'stay away from my little sis' act? It's a bit of an old one of course, but I gotta admit... it's good. _Yeah_. Pretty good."

His sigh is heavy with regrets and nothing less than calculated.

"Don't think I'll listen to you though. See, I have plans for next year now. Things to look forward to. Now _that_ – that hasn't happened in _quite some time_, you know? Looking forward to something."

Moriarty rolls his neck slowly, one way then the other, a theatrical gesture to back up the melodrama leaking off every single one of his words.

"Soooo... request denied! I'd say sorry, but we both know I'm not."

Mycroft grits his teeth.

"Very well. Then I'll have to take measures to make sure things go my way. Consider yourself warned."

Moriarty's grin has a knowing quality to it, and perhaps Mycroft isn't quite in control of his impulses anymore because his next words tumble fast and nasty, a precise waterfall of hatred spilling out to deal a single blow as they reach the helicopter waiting to bring the criminal back to the mainland.

"Enjoy London's New Year festivities this week. You won't see the next ones."

Months later, when Mycroft revisits this moment in his memory palace, the vulnerable slant of Moriarty's smile makes him realise perhaps he never intended to.

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**Hope you enjoyed!**


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